1. Field of the Invention
The present invention relates to sulfur containing cement compositions. More particularly, the invention relates to cement compositions based upon the reaction product of sulfur with derivatives of cyclopentadiene.
2. Description of the Prior Art
The use of sulfur in the preparation of construction materials had been proposed as early as just after World War I when an acid resistant mortar compound of 40% sulfur binder mixed in 60% sand was prepared. However, upon thermal cycling such mortars exhibit a loss in flexural strength resulting in failure of the mortars. The use of sulfur as a binder in the preparation of concretes when combined with an aggregate such as crushed rock or gravel has also been investigated. However, after solidification the sulfur in these concretes undergoes allotropic transformation wherein the sulfur reverts to the more dense orthorhombic form which results in a product that is highly stressed and therefore vulnerable to failure by cracking.
One system which has been involved in a number of investigations is the modification of sulfur with unsaturated hydrocarbon materials, primarily dicyclopentadiene. Several articles show a sulfur cement formulated by blending on the order of several percent to about 15% dicyclopentadiene as a binder with sulfur (W. C. McBee and T. A. Sullivan, Sulphur Institute Journal, Fall 1976; Sulphur Research and Development, 1, (1978) pp. 20-21; Sulphur Institute Journal, Spring 1976, pp. 6-8). Leutner et al., U.S. Pat. No. 4,025,352, show a sulfur cement formulation in which on the order of several percent dicyclopentadiene as a modifier is blended with sulfur. Heating of the blend at temperatures in the range of 120.degree. C. to 160.degree. C. achieves the reaction of sulfur with dicyclopentadiene and a hardened sulfur based cement product is obtained. Gregor and Hackl, New Uses of Sulfur--II, pp. 68-77 (1978) show the use of dicyclopentadiene as a binder for sulfur in sulfur cement formulations and provide data showing the compressive strength and flexural strength characteristics of concrete formulations of the sulfur based cement with aggregate such as basalt and granulit. B. K. Bordoloi and E. M. Pearce, New Uses of Sulfur--II, pp. 31-53 (1978) discuss the copolymerization of sulfur and dicyclopentadiene, particularly with respect to the mechanism by which sulfur reacts with dicyclopentadiene to form polymeric polysulfide products. Vroom, U.S. Pat. No. 4,058,500, shows a somewhat different sulfur based cement formulation in that sulfur is blended with a viscosity increasing, finely divided stabilizer and an olefinic hydrocarbon polymer material as a binder. The reference, however, appears not to include dicyclopentadiene as a hydrocarbon polymeric material because it describes dicyclopentadiene as a prior art binder having a nauseating odor and being toxic at low concentrations, as well as requiring refluxing when it is reacted with sulfur to avoid excessive material loss. Another important disadvantage of dicyclopentadiene as a modifier is that its reaction with sulfur is exothermic and causes a rapid increase in binder viscosity to unworkable levels. Because of this fact very careful preparation of the modifier is necessary which causes considerable operational difficulties on a commercial scale.
Other references which disclose the utilization of dicyclopentadiene as a modifier of sulfur in sulfur cement formulations include Diehl, New Uses For Sulfur and Pyrites, Madrid Symposium of the Sulfur Institute, 1976; McBee et al., Utilization of Secondary Sulfur In Construction Materials, Proceedings of the Fifth Mineral Waste Utilization Symposium, 1976; Sullivan et al., Development and Testing of Superior Sulfur Concretes, 1976 and Sand-Sulfur-Asphalt Paving Materials, 1975 (both Bureau of Mines Reports of Investigations); and Sullivan et al., Sulfur In Coatings and Structural Materials, Advances In Chemistry No. 140. The latter Sullivan et al. reference also shows the use of other olefinic compounds such as dipentene, methylcyclopentadiene, styrene and the like as modifiers in sulfur based cement formulations.
The Welch reference, U.S. Pat. No. 2,806,843, is another relevant prior art reference insofar as it shows cyclodiene sulfo-resins formed by the reaction of sulfur with dicyclopentadiene. The reference broadly shows the reaction of about 25 wt. % to 75 wt. % sulfur with dichclopentadiene or related cyclic diolefin. The reference exemplifies the specific reaction of sulfur with polycyclopentadiene in a 1:1 wt. ratio where the polycyclopentadiene is defined as a mixture of dimer, trimer, tetramer and pentamer products of cyclopentadiene (unspecified proportions). However, the sulfo-resin product obtained has a very high softening point of about 141.degree. C. indicating that the product of the reaction is a highly viscous mass which sets-up during reaction making stirring impossible. The sulfur cement product of the present invention, on the other hand, is a highly fluid material during the reaction of sulfur with the olefinic modifier.
In view of the problems inherent in the use of dicyclopentadiene as a modifier for sulfur based cement formulations, a need continues to exist for a binder for use with sulfur which will yield modified sulfur cement formulations of improved processing and strength characteristics.